1. Technical Field
The present disclosure relates to an equalization method and an equalizer applicable to a radio communication apparatus.
2. Description of the Related Art
In a radio communication apparatus, a transmitter carries out coding of a transmission signal, interleaving, modulation, scrambling, and generation of a symbol signal. Modulation speed in the modulation is referred to as a symbol rate. The transmitter filters the symbol signal to generate a sampled signal, inputs the sampled signal to a mixer with a carrier signal, generates a radio frequency (RF) signal, and transmits the RF signal to a receiver.
To the transmitted RR signal, channel characteristics of a transmission channel and interference are added by the time when the RF signal reaches the receiver, and noise is further added in the receiver.
The receiver carries out mixing of the received RF signal, and then carries out time sampling of a complex signal by an analog-to-digital converter (ADC). The receiver filters the sampled signal, and then converts the filtered signal to a frequency domain signal by a discrete Fourier transformation (DFT) or a fast Fourier transformation (FFT). The receiver equalizes the frequency domain signal, and then converts the equalized signal into a time domain signal by an inverse discrete Fourier transformation (IDFT) or an inverse fast Fourier transformation (IFFT) to obtain a symbol signal. The receiver carries out descrambling of the symbol signal, demodulation, de-interleaving, decoding, and regeneration of the transmitted signal. In the series of processing of the receiver, the equalization eliminates channel characteristics and interference between the transmitter and the receiver.
Examples of equalization according to the related art are described in, for example, Japanese Unexamined Patent Application Publication No. 2006-245810 and Japanese Patent No. 5166246.
Japanese Unexamined Patent Application. Publication No. 2006-245810 describes a technique in which, in a receiver with a single antenna system, when a sampling frequency of an ADC in the receiver is higher than twice the symbol rate (for the purpose of simplification, it is assumed that the sampling frequency is twice the symbol rate), equalization is carried out by combining specific frequencies to calculate equalization coefficients.
Japanese Patent No. 5166246 describes a technique in which, in a receiver with two antenna systems (for the purpose of simplification, the receiver is assumed to have two antenna systems), when the sampling frequency of an ADC in the receiver is twice the symbol rate, equalization is carried out by combining specific frequencies through an inverse matrix operation for a 4×4 matrix, which has complex number elements, to calculate equalization coefficients.